1. Field of the Invention
The device of the present invention generally relates to molded case circuit breakers and, more particularly, to operating mechanisms for controlling the mechanical operation of molded case circuit breakers.
2. Background Information
Circuit breakers and, more particularly, molded case circuit breakers are old and well known in the prior art. Examples of such devices can be found in U.S. Pat. Nos. 3,525,959; 3,614,865; 3,815,059; 3,863,042; 4,077,025; and 4,166,205. In generally, prior art molded case circuit breakers have been provided with moveable contact arrangements and operating mechanisms designed to provide protection for an electrical circuit or system against electrical faults, specifically, electrical overload conditions, low level short circuit or fault current conditions, and, in some cases, high level short circuit or fault current conditions. Prior art devices have utilized a trip mechanism for controlling the movement of an over-center toggle mechanism to separate a pair of electrical contacts upon an overload condition or upon a short circuit or fault current condition. Such trip mechanisms have included a bimetal moveable in response to an overload condition to rotate a trip bar, resulting in the movement of the over-center toggle mechanism to open a pair of electrical circuit breaker contacts. Such prior art devices have also utilized an armature moveable in response to the flow of short circuit or fault current to similarly rotate the trip bar to cause the pair of contacts to separate. At least some prior art devices use blow apart contacts to rapidly interrupt the flow of high level short circuit or fault currents.
While many prior art devices have provided adequate protection against fault conditions in an electrical circuit, a need existed for dimensionally small molded case circuit breakers capable of fast, effective and reliable operation. Many operating mechanisms now used to control the mechanical operation of such circuit breakers require relatively large amounts of operating space. Therefore a need existed for an operating mechanism for molded case circuit breakers that utilizes a relatively small amount of space yet provides fast, effective and reliable operation for protecting an electrical system against overload or fault current conditions. Such a system is described in U.S. Pat. No. 4,540,961, issued Sep. 10, 1985 and assigned to the assignee of this application. While the improvement provided by the foregoing patent met the objective, operating experience has indicated that there is still room for improvement under certain abnormal operating conditions. For example, it has been found that when the contacts are welded, though the handle arm rotation is stopped by hitting a bump on the crossbar, the handle arm lifts up off of its pivot surface allowing the handle arm to move further towards the off position without affecting the desired change of state of the toggle or adding pressure to open the contacts.